Digital computers have employed methods and systems for transferring digital information from memory to various subsystems of the computers, including graphics subsystems. Graphics subsystems control, in part, the graphical display on a computer work station or terminal.
In one prior art configuration, graphical information was first down-loaded into a section of main memory (i.e., host memory) of the computer. The prior art computer had a special-purpose display list processor in addition to a host processor. The computer also had a special-purpose display list memory in addition to the host memory. The display list processor would then transfer the graphical information from the host memory to the display list memory. The display list processor would then send the graphical information from the display list memory to the graphics subsystem by continually traversing the display list.
One disadvantage with this prior art configuration was that it involved two transfers of data--one transfer from the host memory to the display list memory and another transfer from the display list memory to the graphics subsystem--rather than one transfer. This accordingly imposed a performance penalty.
Another disadvantage with this prior art configuration was that it involved extra hardware beyond the host processor and the host memory--namely, the display list processor and the display list memory.
In another prior art configuration, there was no special purpose display list processor and no special purpose display list memory. Instead, the graphical information was stored in the main (i.e., host) memory, and transferred from the main memory to the graphics subsystem by the host processor. The host processor thus took the place of the list processor.
One disadvantage with this latter prior art configuration was that a large portion of the processor's time was devoted to doing these transfers of graphical information from the memory to the graphics subsystem. This delayed the processor from doing other operations. Another disadvantage was that the processor could not keep up with the speed at which the graphics subsystem could receive the data. In other words, the transfers were not as fast as they could be.